An illustration is given for a general structure of a magnetic recording medium including a magnetic tape used for video tape, etc., based on FIG. 1. In the structure, there is formed a magnetic layer 3 via an undercoat layer 2 on one side of a non-magnetic substrate 1, such as polyester, and there is formed a back coating layer 4, to which carbon black for leaking static electricity is added, on one side of the non-magnetic substrate 1 which is the opposite side to the magnetic layer 3. In the necessary case, there is also formed an undercoat layer between the non-magnetic substrate 1 and the back coating layer. That is, the undercoat layer is formed on one side or both sides of the substrate. However, a magnetic recording medium is fundamentally of structure in which a magnetic layer is formed on one side of non-magnetic substrate such as polyester.
Recently, as requirement for a long time recording is called forth, so the magnetic recording medium should be made thin to meet the requirement. However, if the medium is made thin, physical properties such as tensile elastic modulus are decreased, resulting in tendency to tape cutting or edge damage and electromagnetic transformation property is also decreased. To overcome this problem there are used polyethylene naphthalate (PEN), etc., which have a high mechanical strength as a non-magnetic substrate, but satisfactory advantage is so far not obtainable.